The proposed research is directed at understanding how amino acid sequences encode protein folding pathways. The model system is the extremely simple fold adopted by the 58 amino acid IgG binding domain of Peptostreptococcal protein L, a four stranded beta-sheet packed against a single alpha-helix. The research plan involves using the phage display technology to obtain divergent sequences which adopt the fold of IgG binding domain of protein L, identifying the sequences with altered folding behavior, and characterizing the folding pathway of those selected sequences. The research should generate a large amount of information about how a linear amino acid sequence dictates the folding of a protein into a unique three dimensional structure. The results from this model system may help us to the prediction of three dimensional protein structure from amino acid sequence, and the practical modification and design of proteins.